A mode of radio communication known as frequency modulation finds considerable use in both commercial broadcasting and private radio communication systems. As known in the art, a frequency modulated signal is of substantially constant amplitude but varies in frequency about a center frequency by a deviation related to the amplitude of a modulating signal, such as a voice audio signal.
Prior art frequency modulation systems have generally been analog systems which process the modulating signal and generate the frequency deviations in an analog, as opposed to a digital, manner. While such analog systems are generally successful, they are not readily adaptable to integration on integrated circuit chips. As a result, such systems cannot generally take full advantage of the reduced size and cost which integrated circuit technology has to offer. Also, analog systems have a tendency to be unstable, requiring periodic testing and adjustment to make sure that the emitted frequency modulated signals conform to government regulations.
It is therefore a general object of the present invention to provide a new and improved system and method for generating a frequency modulated signal utilizing digital techniques.
It is a further object of the present invention to provide such a system and method which utilizes a frequency shift synthesizer which can be digitally programmed for generating the frequency modulated signal.
It is still a further object of the present invention to provide such a system and method wherein the modulating signal can be pre-processed digitally to provide integrated processing and exact frequency deviation.